Method for welding aluminum article to another metal article



Jan. 27, 1959 M. F. REJDAK v 7 2,870,493

METHOD FOR WELDI NG ALUMINUM ARTICLE TO ANOTHER METAL ARTICLE Filed April 25, 1955 INVENTOR. NELV/N/E'REJDAK BY 06% nwflw A T OENEXS- United States Patent METHOD FOR WELDING ALUMINUM ARTICLE TO ANOTHER METAL ARTICLE Melvin F. Rejdak, Cleveland, Ohio, assignor to Erico Products, Inc., Cleveland, Ohio, a corporation of Ohio Application April 25, 1955, Serial No. 503,569 11 Claims. c1. 22-204 This invention relates as indicated to a novel method and material for welding aluminum and other metals, and more particularly to a cast welding operation utilizing molten metal produced by an exothermic reaction.

In Patent No. 2,229,045 to Charles A. Cadwell, there is disclosed a method of welding copper rail bonds to steel rails utilizing highly heated molten copper produced by an exothermic reaction of the thermit type, and such method has now been in successful commercial use for a number of years on a large scale. Patents 2,277,014 to Noble G. Carlson and 2,654,129 to Edward B. Neif disclose certain preferred forms of cast welding apparatus adapted to be employed with the metal producing exothermic reaction mixture, and in application Serial No. 422,032 of Donald J. Burke for Welding Apparatus filed April 9, 1954, there is disclosed another form of apparatus particularly adapted for the joining together of two opposed cable ends by means of a cast weld connection. a For a great many years, copper wire and cable has been accepted as the standard conductor for electric current although certain other metals such as aluminum and silver have been utilized in special applications where their qualities are particularly desirable. In recent years, however, the use of aluminum wire and cable has very greatly increased, and it often becomes necessary to join aluminum cables together or to connect the same to copper bus bars, for example. The molten metal produced by the exothermic reaction mixture disclosed in the aforesaid Cadwell Patent 2,229,045 has not proved satisfactory for the cast welding of aluminum, and prior to my present invention it has been impossible to obtain a connection which is both physically strong and of substantially unimpaired electrical conductivity.

It is accordingly a principal object of this invention to provide a method and material for east welding aluminum articles, and more especially for cast welding aluminum conductors such as cable to other cable, bus bars, grounds, etc.

Another object is to provide such method of welding which is not hindered by theusual oxide film found on articles of aluminum. 7 I

A further object is to provide such material and method of welding utilizing an exothermic reaction mixture to produce the molten weld metal in situ at the proper temperature and under properly controlled conditions.

Still another object is to provide a cast welded con- I ends, said invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed draw ing setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

Said annexed drawing is a semi-diagrammatic crosssection through a graphite crucible and associated mold cavity adapted to receive two opposed cable ends to be cast welded together.

Referring now more particularly tosuch drawing, the welding apparatus may comprise two graphite blocks such as 1. hollowed out to provide an upper crucible portion 2 and mold cavity portion 3, the two halves being temporarily clamped together as shown and described in Burke application Serial No. 422,032, for example. Two dry and clean cable end portions 4 and 5 are clamped in the mold cavity with their opposed ends located substantially vertically below sprue 6 which is closed by means of a small metal disc 7, ordinarily steel. The exothermic reaction mixture which may be supplied in the form of a cartridge is emptied into the crucible so that the principal metal forming materials 8 fill the lower portion of the crucible and the starting powder 9 forms a layer on top. Such starting powder may then be ignited with a flint gun, and it in turn ignites the exothermic reaction mixture to produce the molten metal charge which melts through disc 7 and drops into mold cavity 3, surrounding the cable end portions and bonding thereto. welded connection removed.

As previously indicated, it has proven extremely difficult to obtain a satisfactory weld where aluminum articles are concerned, as for example when attempting to weld aluminum cable to a copper bus bar. Not only does the aluminum conduct away heat with great rapidity, but also the thin film of aluminum oxide normally covering its surface is highly refractory in character and militates against the obtaining of a true weld in which the metal of the aluminum article is intimately interfused with the weld metal. I have found that a satisfactory weld, and

more particularly a weld of good physical strength and electrical conductivity, may be obtained by the employment of molten tin or tin alloy as the weld metal which is so highly heated that it is effective to melt a portion of the aluminum (including aluminum alloy) article while covering such melted portion and preventing contact with the atmosphere. The thin refractory aluminum oxide film is thus locally flushed away and true interfusion of the underlying aluminum with the weld metal is obtained. a

I have further discovered that such weld metal may desirably be produced by an exothermic reaction between stannic or stannous oxide and sufiicient aluminum to reduce such oxide, sufiicient additional metal being present in the reaction mixture to control the violence of the reaction and to form an alloy with the tin metal produced thereby of proper strength, malleability and electrical conductivity.

I have also discovered that certain selected fluxing agents when incorporated in the exothermic reaction mixture greatly facilitate proper carrying out of the opera tion.

Ordinarily, not only is aluminum the preferred reducing agent for the tin oxide, but it is also the preferred metal for inclusion in the reaction mixture to regulate the reaction and alloy with the molten tin produced thereby.

The basic reaction using stannic oxide may be written as follows:

3SnO +4Al 2Al O +3Sn or stated by parts by weight:

. 37 parts SnO +9 parts Al 26+parts Sn The mold may then be opened and the oneness 2 =1} Using stannous oxide, the reaction may be written:

3SnO+2AllAl O -l-3Sn 32 parts SnO+4 parts Al 28 parts Sn The metallic tin produced by the foregoing reaction is extremely highly heated but the reaction, unless regulated as described below, is so violent and spatters the reaction mixture so exceedingly that it is not practical. I accordingly prefer to incorporate in the reaction mixture an excess of from 8 to 31 parts of aluminum powder based on the parts formula given above. An excess of 17 parts aluminum powder ordinarily yields the best results. This excess aluminum not only serves to moderate, regulate and control the otherwise too violent exothermic reaction, but also alloys with the molten metallic tin produced to form a highly heated molten alloy capable when dropped into the mold cavity of interfusing with the aluminum cable end portions to form a strong malleable cast weld. such molten charge will preferably be in excess of 2,000 F. and the cast weld metal is accordingly enabled actually to melt portions of the cable and wash away the refractory oxide film thereon to form an integral weld. The aluminum cable or other aluminum article may also be cast welded by my new process to articles of brass, bronze, and nichrome. In these cases, both the aluminum article and the other article are interfused with the cast weld metal. Copper, steel, stainless steel and cast iron articles may also be bonded to aluminum articles in accordance with my invention if properly prepared, as by dipping in molten tin, so that the cast weld metal will brazethereto.

By far the preferred fluxing agent which may be included in the exothemic reaction powder mixture is calciurn fluoride. A proportion of cryolite or sodium chloride may be included therewith.

The following examples of suitable exothemic reaction powder formulations for welding aluminum in accordance with my invention are given by way of illustration only and are not to be considered as limiting the invention. They are arranged in order of preference and the percentages given are by weight. In each case aluminum powder is employed as the oxide reducing agent and also as the excess metal included for the purpose of regulating the reaction:

Example 1 Percent Tin oxide 56.0 Aluminum powder 39.4 Calcium fluoride 3.0 Cryolite 1.6 Example 2 Tin oxide 65.0 Aluminum powder 245 Calcium fluoride 10.5

Example 3 Tin oxide 61.8 Aluminum powder 28.4 Calcium fluoride 6.6 Cryolite 3.2

Example 4 Tin oxide 58.8 Aluminum powder 36.5 Calcium fluoride M 3.6 Cryolite 1.]

Example 5 Tin oxide 57.8 Aluminum powder 39.0 Calcium fluoride 1.6 Sodium chloride 1.6

T he temperature of Example 6 Tin oxide 54.4 Aluminum powder 42.6 Calcium fluoride 1.4 Cryolite 1.6 Example 7 Tin oxide 47.4 Aluminum powder 50.0 Calcium fluoride 1.3 Sodium chloride 1.3

As previously indicated, certain other metals may be included in the exothermic reaction mixture for the purpose of regulating the same instead of the excess aluminum provided in the examples given above. In general, an amount of aluminum powder will be included slightly more than the theoretical amount required to reduce the tin oxide present and then approximately 20% by weight of nickel, tin, silver, iron, or chromium may be included instead of the excess aluminum. Of course, when tin metal constitutes such excess, the resultant molten charge will be substantially entirely tin with only quite small amounts of aluminum, iron, etc. Illustrative examples of exothermic reaction mixture formulations in accordance with my invention in which a metal other than aluminum is utilized to control the reaction and to alloy with the molten tin produced are given below:

Example 8 Percent Tin oxide 59.5 Aluminum powder 14.7 Silver 21.0 Calcium fluoride 3.2 Cryolite 1.6 Example9 Tin oxide 60.5 Aluminum powder 14.5 Nickel 19.7 Calcium fluoride 3.3 Cryolite 2.0

Example 10 Tin oxide 60.5 Aluminum powder 14.8 Iron 18.0 Calcium fluoride 6.7

Example 11 Tin oxide 58.5 Aluminum powder 14.3 Tin 22.2 Calcium fluoride 3.2 Cryolite 1.8

Example 12 Tin oxide 61.8 Aluminum powder 14.7 Chromium 13.6 Calcium fluoride 9.9

Stannic oxide is commercially available in particle sizes of from about 0.5 to about 1.5 microns, and such material has proven very satisfactory for my purpose although somewhat larger size particles are also suitable. A suitable particle size for the aluminum powder and other metals present in the reaction mixture is approximately 325 mesh. It will be appreciated that the excess metals employed for the purpose of regulating the reaction may include one or more of the several metals indicated above as suitable for this purpose. The principal requirement is that they shall not be volatilized by the heat of the reaction and will alloy with the molten tin to form a strong malleable cast weld of good electrical conductivity.

Various other suitable ignition mixtures are well known in the art. They may themselves be ignited in various ways, the safestand most satisfactory being through use of aflint gun.

In general, other reducing agents known and employed in various prior art thermit reactions are not nearly as satisfactory as aluminum, some of them producing reactions even more diflicult to control and forming less satisfactory alloys with the metal tin. Consequently, aluminum is by far the preferred reducing agent.

The preferred alloying metals indicated above have relatively high boiling points, high latent heats of fusion and are capable of alloying with the tin to form malleable cast welds with good electrical conductivity. The alloying metals should have boiling points not lower than 3500 F. The most suitable alloying metals listed above have boiling points as follows:

F. Silver 4010 Nickel 4950 Iron 4960 Tin 4120 Chromium 4500 Aluminum 3740 Aluminum has a melting point of 1220 F. and tin has a melting point of 449 F. The alloys produced by reaction of the exothermic reaction mixtures listed above all have melting points below 2000 F.

It will be seen from the foregoing that I have provided a novel exothermic reaction mixture which permits me to weld an aluminum article to another metal article by igniting such exothermic reaction mixture to produce highly heated molten tin or an alloy thereof having a temperature in excess of 2000 R, such molten metal immediately being delivered to a mold cavity defined in part by such articles to be joined, the heat content of such molten charge causing a portion of the aluminum article to interfuse therewith to form a strong malleable connection. In certain cases, the heat of such molten charge may be as high as 3000 F.

Stannous oxide, while also suitable for use in the reaction, is too expensive for ordinary commercial use. The specific examples given above accordingly employ the stannic oxide. The molten metal produced by my exothermic reaction will ordinarily and preferably comprise a major proportion of tin by weight.

Certain subject matter disclosed but not claimed herein is disclosed and claimed in my co-pending divisional application Serial No. 728,279, filed April 14, 1958.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

I therefore particularly point out and distinctly claim as my invention:

1. The method of Welding an aluminum article to another metal article which comprises exothermioally redwcing tin oxide with metallic aluminum, controlling the violence of the reaction by inclusion of excess aluminum in the exothermic reaction mixture, such excess aluminum alloying with the molten tin produced, immediately delivering such resultant molten alloy at a temperature of at least 2,000 F. to a mold cavity defined in part by such articles to be welded, the heat content of such molten charge being sufficient partially to melt such aluminum stainless steel and cast iron, the'molten 6 article for interfusion therewith to form a strong malle able cast weld connection of good electrical conductivity. 2. The method of claim 1, whereinthe other metal article is selected from the class consisting of aluminum, brass, bronze, and nichrome, the molten alloy forming an interfused cast weld connection therewith.

3. The method of claim 1, wherein the other metal article is selected from the class consisting of copper, steel, alloy forming a brazed connection thereto. l i j 4. In the method of welding a metal part to an aluminum article ,having an aluminum oxide coating thereon; producing highlyheated molten tin by an exothermic reaction and contacting such article with such molten tinat a temperature in excess of 2,000 F. s ufiicient to melt the opposed surface of such article, such oxide coating in the region of contact being dissipated and such tin and aluminum forming an interfused cast Weld.

5. In the method of welding a metal part to an aluminum article having an aluminum oxide coating thereon; producing highly heated molten tin by an exothermic reaction, alloying aluminum therewith to form a molten alloy having a temperature above 2,000 F., and contacting such article with such hot molten alloy to melt the opposed surface of such article, such oxide coating in the region of contact being dissipated and such molten alloy and aluminum article forming an interfused cast weld.

6. In the method of welding a metal part to an aluminum article having an aluminum oxide coating thereon; producing highly heated molten tin by an exothermic reaction, alloying 'silver therewith to form a molten alloy having a temperature above 2,000 F., and contacting such article with such hot molten alloy to melt the opposed surface of such article, such oxide coating in the region of contact being dissipated and such molten alloy and aluminum article forming an interfused cast weld.

7. In the method of welding a metal part to an aluminum article having an aluminum oxide coating thereon; producing highly heated molten tin by an exothermic reaction, alloying nickel therewith to form a molten alloy having a temperature above 2,000 F., and contacting such article with such hot molten alloy to melt the opposed surface of such article, such oxide coating in the region of contact being dissipated and such molten alloy and aluminum article forming an interfused cast weld.

8. In the method of welding a metal part to an aluminum article having an aluminum oxide coating thereon; producing highly heated molten tin by an exothermic reaction, alloying iron therewith to form a molten alloy having a temperature above 2,000 F., and contacting such article with such hot molten alloy to melt the opposed surface of such article, such oxide coating in the region of contact being dissipated and such molten alloy and aluminum article forming an interfused cast weld.

9. In the method of welding a metal part to an aluminum article having an aluminum oxide coating thereon; producing highly heated molten tin by an exothermic reaction, alloying chromium therewith to form a molten alloy having a temperature above 2,000 F., and contacting such article with such hot molten alloy to melt the opposed surface of such article, such oxide coating in the region of contact being dissipated and such molten al1c1 y and aluminum article forming an interfused cast we d.

10. In the method of welding a metal part to an aluminum article having an aluminum oxide coating thereon; producing highly heated molten tin by an exothermic reaction, melting tin metal by the heat of such reaction and simultaneously combining the same with the molten tin produced by the reaction to form a charge of molten tin having a temperature of at least 2,000 F., and contacting such article with such hot molten charge to melt the opposed surface of such article, such oxide coating in the region of contact being dissipated and such molten charge and aluminum article forming an interfused cast weld.

11. In the method of welding a metal part to an aluminum article having an aluminum oxide coating thereon; producing highly heated molten tin by an exothermic reaction, alloying a metal therewith effective to lower the temperature of such molten tin and produce an alloy of good strength, malleability and electrical conductivity when hardened, such alloy comprising a major proportion of tin by weight and in its molten state as thus produced having a temperature of at least 2,000 E, contacting such article with such molten alloy to melt the opposed surface of such article, such oxide coating in the region of contact being dissipated and such molten alloy and aluminum article forming an interfused cast weld.

References Cited in the file of this patent UNITED STATES PATENTS Monnot May 14, 1907 Page Feb. 22, 191 0 Heinkel et al 1. Nov. 12, 1912 Metzl Feb. 18, 1913 Lapotterie Apr. 18, 1916 FOREIGN PATENTS 7 Great Britain July 18, 1922 France Jan. 24, 1949 Sweden Dec. 13, 1955 

1. THE METHOD OF WELDING AN ALUMINUM ARTICLE TO ANOTHER METAL ARTICLE WHICH COMPRISES EXOTHERMICALLY REDUCING TIN OXIDE WITH METALLIC ALUMINUM, CONTROLLING THE VIOLENCE OF THE REACTION BY INCLUSION OF EXCESS ALUMINUM IN THE EXOTHERMIC REACTION MIXTURE, SUCH EXCESS ALUMINUM ALLOYING WITH THE MOLTEN TIN PRODUCED, IMMEDIATELY DELIVERING SUCH RESULTANT MOLTEN ALLOY AT A TEMPERATURE OF AT LEAST 2,000* F. TO A MOLD CAVITY DEFINED IN PART BY SUCH ARTICLES TO BE WELDED, THE HEAT CONTENT OF SUCH MOLTEN CHARGE BEING SUFFICIENT PARTIALLY TO MELT SUCH ALUMINUM ARTICLE FOR INTERFUSION THEREWITH TO FORM A STRONG MALLEABLE CAST WELD CONNECTION OF GOOD ELECTRICAL CONDUCTIVITY. 